Hi Jan, does this feature require manual QA?
If that is the case, could you please advise on how should I proceed with the validation of this feature? The following aspects would be very useful:
1. Automation coverage for this feature.
2. Things to keep in mind while verifying and performing regression testing.
3. Anything else you think that might help me verify this feature.

(In reply to Andrei Vaida, QA [:AndreiVaida] from comment #18)
> Hi Jan, does this feature require manual QA?
>
> If that is the case, could you please advise on how should I proceed with
> the validation of this feature? The following aspects would be very useful:
> 1. Automation coverage for this feature.
> 2. Things to keep in mind while verifying and performing regression testing.
> 3. Anything else you think that might help me verify this feature.
(a) Adding Automated testing is tracked in Bug 949525
(b) Manual verification can be done i.e. with content/media/test/vp9.webm
to verify visually that it plays back correctly. (once Bug 949525 is fixed)

Thank you Jan. I was able to successfully verify this feature using the latest Aurora (BuildID: 20131213004002) on Windows 7 x64, Mac OS X 10.9 and Ubuntu 13.10 x64, with the files "vp9cake.webm" and "vp9.webm" from Bug 949525.
Also, I'm not sure if the following notes are relevant at this point, but I thought they were worth mentioning:
- Google Chrome cannot playback the two *.webm files attached to Bug 949525.
- http://www.youtube.com/html5 states that the latest Aurora does not support "MSE & WebM VP9".
I will test this feature further when additional test files will be available.

Jan, I noticed that all the VP9-encoded test files previously attached to Bug 949525 are currently marked as obsolete. Are there any new video samples available for testing purposes? Or maybe a page featuring an embedded video of the same format?

(In reply to Andrei Vaida, QA [:AndreiVaida] from comment #23)
> Jan, I noticed that all the VP9-encoded test files previously attached to
> Bug 949525 are currently marked as obsolete. Are there any new video samples
> available for testing purposes? Or maybe a page featuring an embedded video
> of the same format?http://base-n.de/webm/VP9%20Sample.html

(In reply to Andrei Vaida, QA [:AndreiVaida] from comment #23)
> Jan, I noticed that all the VP9-encoded test files previously attached to
> Bug 949525 are currently marked as obsolete. Are there any new video samples
> available for testing purposes? Or maybe a page featuring an embedded video
> of the same format?
The files attached to Bug 949525 are still good test files,
they are part of the automated test suite and only marked
as obsolete since they where included in the patch that got committed: https://bugzilla.mozilla.org/show_bug.cgi?id=949525#c10

The feature was thoroughly tested and all the associated test cases were successfully executed, uncovering minor issues only.
The latest smoke tests performed on Firefox 28 Beta 1 also uncovered no major issues.

It's not normal that after disabling "media.webm.enabled" and "media.encoder.webm.enabled" youtube shows that MSE & WebM VP9 is supported and videos start to play in webm/VP9 format, right?
("WebM VP8" is shown to be not supported)

(In reply to Anthony Jones (:kentuckyfriedtakahe, :k17e) from comment #34)
> Try setting media.mediasource.enabled to false.
But what if I only want to disable VP9. Which is a valid reason because it has exorbitant CPU usage and no hardware acceleration, and as such is unplayable.
Disabling whole webm is already a sacrifice, but not a great one since youtube (the de facto web video site) mostly moved to VP9.
But if I disable MSE too I loose most of the higher resolution/quality videos.
(Ignoring the fact that for now since bug 1027875 landed both vp9 and AVC youtube videos play without audio and only for 32 seconds.)

(In reply to avada from comment #33)
> It's not normal that after disabling "media.webm.enabled" and
> "media.encoder.webm.enabled" youtube shows that MSE & WebM VP9 is supported
> and videos start to play in webm/VP9 format, right?
That does sounds like an oversight. If you'd like it to apply both (or have separate prefs for each codec) please file a new bug. That's easier to track than followup on old, fixed bugs.

(In reply to avada from comment #35)
> But what if I only want to disable VP9. Which is a valid reason because it
> has exorbitant CPU usage and no hardware acceleration, and as such is
> unplayable.
> Disabling whole webm is already a sacrifice, but not a great one since
> youtube (the de facto web video site) mostly moved to VP9.
> But if I disable MSE too I loose most of the higher resolution/quality
> videos.
MP4 does not work with MSE yet so you should disable MSE if you don't want WebM.

(In reply to Ralph Giles (:rillian) from comment #36)
> That does sounds like an oversight. If you'd like it to apply both (or have
> separate prefs for each codec) please file a new bug. That's easier to track
> than followup on old, fixed bugs.Bug 1035622 now covers this.(In reply to Anthony Jones (:kentuckyfriedtakahe, :k17e) from comment #37)

Dear friends,
I have to ask you if vp9 could be used on opera 10 browser.
My old computer does not support more than opera 10, it's intel p3 800 mhz with 256 sdram for moment.
Os works best on those old pc is windows millenium.
Sure I could instal win xp on that, but works hard ansee video from youtube for example.
I need some advices from you if you know what I should do or install.
Thank you very much in advance.
My email is medichit@gmail.com

(In reply to Clemens Eisserer from comment #41)
> Any idea, what I still only get VP8 videos with FF36 on youtube limited to
> 360p, while Chrome receives VP9 streams with up to 1080p?
>
> Also on youtube.com/html5 I get "MSE & WebM VP9" = disabled.
The place for support is support.mozilla.org
Anyway, because it's disabled, because it's not fully enable implemented.media.mediasource.enabled in about:config. Then you'll get all resolutions.

(In reply to avada from comment #42)
> The place for support is support.mozilla.org
> Anyway, because it's disabled, because it's not fully enable
> implemented.media.mediasource.enabled in about:config. Then you'll get all
> resolutions.
Well this got effed... Supposed to be "enable media.mediasource.enabled"

Hmm, even with enable media.mediasource.enabled, VP9 playback on Youtube has all kinds of issues on Linux.
Unfortunately it seems, Firefox is not a good choice for youtube.com-users running Linux currently :/

(In reply to Clemens Eisserer from comment #47)
> Unfortunately it seems, Firefox is not a good choice for youtube.com-users
> running Linux currently :/
I just use the HTML5 Video Everywhere addon to force Firefox's built in video player instead of YouTube's crappy one and I've disabled webm and set it to only use mp4. Works fantastically better. YMMV
A new bug for Linux issues should probably be filed instead of commenting here further.

For those wondering how to enable MSE & WebM VP9 in Firefox nightly, you must leave:
media.webm.enabled=true (default)
media.mediasource.enabled=true (default)
You must change:
media.mediasource.webm.enabled=true (user-set)

(In reply to Scott Baker from comment #51)
> Are the directions in #49 platform agnostic? Or are they Windows specific? I
> want to get this working under Linux.
All the webm stuff is generally platform agnostic. The decoder is built-into Firefox. It's just the h.264 & mp3 stuff that's platform dependent.

(In reply to Scott Baker from comment #53)
> I should have been more specific. Are the MediaSource options platform
> agnostic?
The same prefs need to be set as in comment 49, but one is defaulted to off still. If you turn it all on it should work though. (youtube.com/html5 says "MSE & WebM VP9" is enabled for me, at least)

(In reply to Dave Garrett from comment #54)
> (In reply to Scott Baker from comment #53)
> > I should have been more specific. Are the MediaSource options platform
> > agnostic?
>
> The same prefs need to be set as in comment 49, but one is defaulted to off
> still. If you turn it all on it should work though. (youtube.com/html5 says
> "MSE & WebM VP9" is enabled for me, at least)
Same here. Also, if you right click you can click on the video, click on "stats for nerds" and you will see the codec is vp9 (assuming the video exists in vp9).

At least for me, youtube with VP9 doesn't work reliable in Firefox.
From time to time clips don't continue loading and are stuck at e.g. 30%, also when jumping inside a clip it quite often simply does not play any further after some jumps.

(In reply to Clemens Eisserer from comment #56)
> At least for me, youtube with VP9 doesn't work reliable in Firefox.
> From time to time clips don't continue loading and are stuck at e.g. 30%,
> also when jumping inside a clip it quite often simply does not play any
> further after some jumps.
I haven't seen that, yet. What are your PC specs, out of curiosity?

(In reply to Clemens Eisserer from comment #56)
> At least for me, youtube with VP9 doesn't work reliable in Firefox.
> From time to time clips don't continue loading and are stuck at e.g. 30%,
> also when jumping inside a clip it quite often simply does not play any
> further after some jumps.
That is why it is disabled in nightly.

something bad about MSE & Webm VP9 is that youtube only delivers VP8 360p :/
so that I need to enforce the Flash Player on Linux to get better quality
Is someone still working on this? (since the last post is from april)

(In reply to Djfe from comment #60)
> Is someone still working on this? (since the last post is from april)
This feature is VP9 support in Firefox and is complete hence the closed bug and no further comments in this bug. MSE support is being tracked in bug 778617.